It has been well documented that one negative of
air travel — besides the food — is the emission of CO2 from jet
engines. But what about contrails?

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Dr. Emma
Irvine, Professor Keith Shine, and Professor Sir Brian Hoskins, at the
Department of Meteorology at the University of Reading have linked contrails to
global climate change in a study published in IOP Publishing's journal Environmental Research Letters.

According
to their report, contrails may have a greater radiative forcing (the capacity
for an agent to enact climate change via warming) than CO­2.

Contrails are the visible trails of condensed water
vapor that form from aircraft at high altitudes, making their effects on the atmosphere
similar to those of clouds. Contrails work to increase Earth's albedo,
reflecting incoming short-wave radiation from the sun and cooling the earth. However,
contrails also act as a greenhouse gas to trap outgoing long-wave radiation and
heat the earth. Measurements have been made in support of the latter
outweighing the former, making contrails an agent of global warming.

Therefore, Dr. Irvine et al. discuss the possible
trade-off between contrails and CO2, suggesting that there is a way
to minimize radiative forcing by re-routing planes. Their argument is laid out
as follows:

Contrails form predominantly near high-pressure
systems with cold, moist air. Specifically, these are ice-supersaturated
regions (ISSRs) — many of which coincide with the heavily-trafficked North
Atlantic. Research predicts that if a plane leaving from New York City were to deviate
slightly from its flight path to London in order to avoid a region where
contrails form, the plane could reduce its effect on global warming at the cost
of a little more fuel.

Still, the relative impact on climate change from
contrails and CO2 is challenging to predict. There are too many
variables lost in the clouds.

For example, smaller planes can travel farther out
of their way to avoid ISSRs than larger planes and use the same amount of fuel.
Also, planes could avoid fuel-efficient cruising altitudes where contrails form
in favor of lower altitudes where they don't. This multiplicity makes it
difficult for a practical model to be put in place.

Another concern is uncertainty. The world does not
have the infrastructure to monitor the formation of contrails — which have less-than-one-day
lifespans. Neither does the world have precision to map flight-by-flight
weather patterns for the potential of contrail-formation associated with
ascending air in high-pressure systems.

What we do have, courtesy of Dr. Irvine et al., is a
basic model to further look into the conundrum that is contrails.